Evaluation of Static and Dynamic Performance of Externally Pressurized Gas-Lubricated Journal Bearings Using Static, Impact, and Imbalance Loads

Gas film bearings support high-speed mictroturbomachinery with increased efficiency and reliability, coupled with longer maintenance cycles and a reduction in environmental contaminants compared to conventional mineral oil-lubricated bearings. Externally pressurized porous carbon gas-lubricated bearings provide rotor support during static or startup conditions and have high lubricity and resilience in the case of a contact event at operating speeds. This paper presents a combination of static, impact, and imbalance loading experiments to characterize the static and dynamic performance of externally pressurized porous carbon gas radial bearings supporting a test rotor across a range of operating speeds and air supply pressures. The resulting stiffness and damping data was compared against a bearing finite element predictive tool. The static load test identified the system’s stiffness at 0 Hz by applying linear and cubic curve fits to the resulting force-displacement curves. Both schemes yielded stiffness estimates between 2–5 MN/m with correlation values greater than 90%. Bearing static stiffness estimates are in good agreement with the results of impact and imbalance load tests. The impact load test identified frequency-dependent direct stiffness and damping coefficients up to 200 Hz with a stationary rotor. Linearly independent forces were applied directly to the rotor with a calibrated impact hammer in X and Y directions at both ends of the rotor. Matching to the imbalance test data yielded estimates of speed-dependent direct stiffness and damping coefficients, which were validated using a commercial rotordynamic software. Speed-dependent force coefficients are in good agreement to those estimated using the static loading and impact loading parameter identification techniques.